1. Field of the Invention
The present invention relates to a hard disk drive (HDD), and more particularly, to a method and apparatus for optimizing write properties of a magnetic head in consideration of writability of each magnetic head in an HDD, and a method and apparatus for defining the magnetic head.
2. Description of the Related Art
A hard disk drive (HDD) is a device that reads and writes data from and to a disk by way of a magnetic head. The disk is rotatably mounted on a spindle motor, and information is accessed by the magnetic head, namely, a read/write head, mounted on an actuator arm that is rotated by a voice coil motor. The voice coil motor is excited by current to rotate an actuator and move the read/write head. The read/write head detects the occurrence of a magnetic change on a surface of the disk and reads the information recorded on the surface of the disk. To write information on a data track, current is supplied to the read/write head, creating a magnetic field, thereby magnetizing the surface of the disk.
The performance of the HDD under certain environmental conditions is critical in the reliability of the HDD. In particular, the performance of the HDD under certain temperature and humidity conditions is closely related to writability hindrances, such as adjacent track erase (ATE) or weak write (WW) occurrences.
Here, a phenomenon where data written on tracks adjacent to a target track is erased due to write current provided to the magnetic head is referred to as the ATE.
The writability is critical for the HDD, and such write performance can be affected by the environment surrounding the HDD.
In general, at a low temperature, coercivity of a CoCrPt-based magnetic layer of a medium, e.g., a hard disk, increases such that write properties deteriorate, as compared to the operation of the HDD at normal temperatures. Consequently, the HDD cannot correctly write data, and the HDD also suffers deterioration of overwrite properties, thereby failing to correctly overwrite previous data. In contrast, at a high temperature, coercivity decreases such that the HDD is forced to execute too strong of a write current on a same write field. Consequently, the HDD suffers track encroachment (TE) on adjacent tracks, or ATE.
At a high temperature, the ATE properties of the magnetic head deteriorate due to a decrease in the coercivity of the magnetic layer of the medium and in flying height (FH). At a low temperature, however, the ATE properties deteriorate due to an increase in the coercivity of the medium.
As the capacity of an HDD has increased recently, the size of a read/write sensor for the magnetic head has also been reduced, along with the FH. Accordingly, when the physical size of the magnetic head is reduced, the HDD becomes more susceptible to an ATE phenomenon, where data on adjacent tracks is erased due to the strength of the write current provided to the magnetic head.
Here, the occurrence of WW is noticed mostly with low temperatures, i.e., low temperature WW, where magnetic coercivity of a medium increases in the low temperatures such that write properties deteriorate and wrong information is recorded to the disk.
There have been recent attempts to compensate for or correct interference between tracks, i.e., track erasure (TE) or ATE, caused by a decrease in the coercivity of the magnetic layer of the medium at a high temperature, by reducing an over shoot control (OSC) or write current (WC) value. In this case, high temperature WW, which is caused by the OSC or WC being too low in comparison with the property of the magnetic head, may occur.
Here, referring to FIG. 1, illustrating a write current waveform, the write current rises sharply at a turning point from data 2a written on a magnetic layer 1 of a medium to data 2b. A dc component of the write current is referred to as the WC value, and a rising component is referred to as the OSC value. The WC is used to keep the intensity of a magnetic field around the coercivity level of the magnetic layer. The OSC is used to trigger a raising of the intensity of the magnetic field in a recording position beyond the coercivity level.
Most HDDs currently employ the technology that measures a die temperature using a temperature sensor, embedded in a preamplifier, to know an environmental temperature of the HDD, such that, at a low temperature, the OSC and/or WC values may be increased correspondingly to the coercivity of the magnetic layer, which has been enhanced to improve writability, and at a high temperature, the OSC and/or WC values may be decreased correspondingly to the coercivity of the magnetic layer, which has been reduced to have write properties suited to the environmental temperature.
That is, the HDD currently controls the WC and/or OSC through a measuring of the temperature of the HDD, i.e., practically, measuring the temperature of the terminal preamplifier, such that higher WC and OSC values are used at the low temperature to deal with the increase of the coercivity of the magnetic layer and such that the lower WC and OSC values are used at the high temperature to deal with the decrease of the coercivity of the magnetic layer.
However, since the magnetic head and the preamplifier have wide property distributions, the overwrite or writability properties are still not sufficient when the OSC and WC values are increased or decreased to some degree, based only on the detected temperature, as in the conventional art. As a result, low or high temperature WW problems still occur, thereby leading to bit errors or corruption in recorded data.